CN112055196B - Synchronous acquisition time interval measuring method for two cameras based on light flicker - Google Patents
Synchronous acquisition time interval measuring method for two cameras based on light flicker Download PDFInfo
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- CN112055196B CN112055196B CN202010870463.9A CN202010870463A CN112055196B CN 112055196 B CN112055196 B CN 112055196B CN 202010870463 A CN202010870463 A CN 202010870463A CN 112055196 B CN112055196 B CN 112055196B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
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- H04N17/002—Diagnosis, testing or measuring for television systems or their details for television cameras
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Abstract
The invention discloses a method for measuring synchronous acquisition time interval of two cameras based on lamplight flicker. Step 1: connecting two cameras with a computer respectively to form a binocular vision system; step 2: placing the binocular vision system indoors, isolating natural light and setting a flicker light source; and step 3: respectively setting parameters of the cameras, and aligning lenses of the two cameras to a static object; and 4, step 4: controlling two cameras to synchronously acquire images by using a computer; and 5: making the acquired images into average gray curves of two cameras; step 6: whether the acquisition frequency of the two cameras is stable or not is analyzed, and the synchronous acquisition time interval of the two cameras is calculated. The method is used for solving the problem that the system time when the image data is transmitted to the cache of the computer is taken as the image acquisition time of the camera; however, the time is not reliable, various delays occur in the data transmission process, and the problem that the image acquisition time interval of the camera is not accurate when the image acquisition time recorded by the computer is calculated.
Description
Technical Field
The invention belongs to the technical field of binocular vision measurement; in particular to a synchronous acquisition time interval measuring method of two cameras based on light flicker.
Background
When the stereo vision measurement is carried out, the two cameras need to be controlled to be triggered synchronously, but in the practical process, the image acquisition time of the two cameras is not completely consistent. When the cameras acquire images at a higher frequency, the time difference between the two cameras for image acquisition needs to be controlled in a smaller interval, which requires that the system has higher synchronization performance.
The basis for evaluating the synchronization performance is to accurately obtain the camera image acquisition time. The system time when the image data is transferred to the computer buffer is generally taken as the camera image acquisition time. However, this time is not reliable, various delays may occur in the data transmission process, and the calculation of the camera image acquisition time interval from the image acquisition time recorded by the computer is not accurate.
Disclosure of Invention
The invention provides a method for measuring synchronous acquisition time interval of two cameras based on light flicker, which is used for solving the problem that the system time when image data is generally transmitted to a computer for caching is taken as the image acquisition time of the camera; however, the time is not reliable, various delays can occur in the data transmission process, and the problem that the image acquisition time interval of the camera is not accurate when the image acquisition time recorded by the computer is calculated.
The invention is realized by the following technical scheme:
a light flicker-based two-camera synchronous acquisition time interval measurement method comprises the following steps,
step 1: connecting two cameras with a computer respectively to form a binocular vision system;
step 2: placing the binocular vision system indoors, isolating natural light and setting a flicker light source;
and step 3: respectively setting parameters of the two cameras, aligning lenses of the cameras to a static object to ensure that the imaging contents of the two cameras are the same, wherein the parameters are acquisition frequency and exposure time;
and 4, step 4: controlling two cameras to synchronously acquire images by using a computer;
and 5: making the acquired images into average gray curves of the two cameras;
step 6: and 5, analyzing whether the acquisition frequency of the two-phase machine is stable or not through the average gray curve in the step 5, and calculating the synchronous acquisition time interval of the two-phase machine.
Further, in the step 3, the acquisition frequency is 100Hz, and the exposure time is less than 3ms.
Further, the step 6 of analyzing the average gray curve specifically includes taking the average gray of the collected image as a sampling signal, and taking the brightness change of the light as an original signal; if the frequency of the camera is stable and the frequency of the lamplight is stable, the sampling frequency of the camera is lower than 2 times of the frequency of the original signal, and the sampling aliasing occurs according to the sampling theorem; the aliasing frequency is determined by the following equation,
wherein, f a Is the aliasing frequency; f. of s Is the original frequency; SF is the sampling frequency of the camera; int denotes a rounding function, which is an integer part of a reserved number;
n a with a value of 1, the aliasing frequency f a Satisfies the formula:
f a ＝|f s -SF| (2)
and judging whether the acquisition frequency of the camera is stable according to whether the average gray curve is smooth or not.
Further, the average gray scale of the images acquired by the two cameras is at the aliasing frequency f a Making periodic variation; the average gray level curves of the images obtained by the two cameras are not overlapped, and the two curves have phase difference; assuming a phase difference of
When the images are synchronously acquired, the time interval between the two cameras for acquiring the images is delta T a (ii) a The period of light flicker is T a (ii) a If the time interval of the synchronous acquisition of the camera is less than T a Then, there are:
let the camera collect the change of brightness of the image by N t The image is one period, and the phase difference N of the average gray curve of the images collected by the two cameras a One image, the time interval between the two cameras for collecting the images is delta T a Expressed as:
in one curve, the difference of the serial numbers of two adjacent minimum value points corresponds to the length of an aliasing signal period; the difference of the sequence numbers of the minimum value points of the left camera and the right camera corresponds to the phase difference of the aliasing signals; the synchronous acquisition time interval of the two cameras is calculated by equation (4).
The invention has the beneficial effects that:
by utilizing the characteristic that the light flicker frequency is 100Hz, the method for effectively measuring the synchronous acquisition time interval of the two cameras is provided. When the acquisition frequency of the camera is close to the flicker frequency of the light, the image acquired by the camera can have periodic brightness change due to sampling aliasing. The phase difference of the aliasing signals is acquired by the two cameras, so that the time interval of synchronous acquisition can be calculated. The method is simple and easy to use, has low requirement on equipment, and can achieve higher measurement precision.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Fig. 2 is a schematic view of the binocular vision system of the present invention.
FIG. 3 is a graph showing the periodical brightness change of an image according to the present invention, wherein (a) - (f) are images showing the periodical brightness change of the image in a period
FIG. 4 is a graph of the average gray scale of the images of the present invention, (a) the graph of the average gray scale of the image of group 1, (b) the graph of the average gray scale of the image of group 2, (c) the graph of the average gray scale of the image of group 3, (d) the graph of the average gray scale of the image of group 4, (e) the graph of the average gray scale of the image of group 5, and (f) the graph of the average gray scale of the image of group 6.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1
As shown in fig. 1, a lamp light flicker-based two-camera synchronous acquisition time interval measurement method includes the following steps,
step 1: connecting two cameras with a computer respectively to form a binocular vision system;
step 2: placing the binocular vision system indoors, isolating natural light and setting a flicker light source;
and step 3: respectively setting parameters of the two cameras, aligning lenses of the cameras to a static object to ensure that the imaging contents of the two cameras are the same, wherein the parameters are acquisition frequency and exposure time;
and 4, step 4: controlling two cameras to synchronously acquire images by using a computer;
and 5: making the acquired images into average gray curves of the two cameras;
step 6: and 5, analyzing whether the acquisition frequency of the two-phase machine is stable or not through the average gray curve in the step 5, and calculating the synchronous acquisition time interval of the two-phase machine.
Further, in the step 3, the acquisition frequency is 100Hz, and the exposure time is less than 3ms.
Further, the step 6 of analyzing the average gray curve specifically includes taking the average gray of the collected image as a sampling signal, and taking the brightness change of the light as an original signal; if the frequency of the camera is stable and the frequency of the lamplight is stable, the sampling frequency of the camera is lower than 2 times of the frequency of the original signal, and the sampling aliasing occurs according to the sampling theorem; the aliasing frequency is determined by the following equation,
wherein, f a Is the aliasing frequency; f. of s The original frequency is the frequency of the light flicker; SF is the sampling frequency of the camera; int denotes a rounding function, which is an integer part of a reserved number;
n a with a value of 1, the aliasing frequency f a Satisfies the formula:
f a ＝|f s -SF| (2)
and judging whether the acquisition frequency of the camera is stable according to whether the average gray curve is smooth or not.
Further, the average gray scale of the images collected by the two cameras is calculated by aliasing frequency f a Making periodic variation; however, the images acquired by the two cameras cannot be completely synchronized, the average gray level curves of the images acquired by the two cameras are not coincident, and the two curves have phasesA potential difference; assuming a phase difference of
When the images are synchronously acquired, the time interval between the two cameras for acquiring the images is delta T a (ii) a The period of light flicker is T a (ii) a If the time interval of the synchronous acquisition of the camera is less than T a Then, there are:
let the camera collect the change of brightness of the image by N t The image is one period, and the phase difference N of the average gray curve of the images collected by the two cameras a One image, the time interval between the two cameras for collecting the images is delta T a Expressed as:
in one curve, the difference of the serial numbers of two adjacent minimum value points corresponds to the length of an aliasing signal period; the difference of the sequence numbers of the minimum value points of the left camera and the right camera corresponds to the phase difference of the aliasing signals; the synchronous acquisition time interval of the two cameras is calculated by equation (4).
The invention provides a method for measuring synchronous acquisition time interval of two cameras by utilizing light flicker.
Example 2
The two cameras are connected with a computer, and the cameras are controlled by the computer to form a binocular vision system. The two cameras are named as a left camera and a right camera respectively. Isolating natural light. The power supply of the lighting lamp is 220V alternating current, the alternating current frequency is 50Hz, and the lamp light flicker frequency is 100Hz. The camera is aimed at the wall as shown in fig. 2.
The image is acquired in a soft-triggered manner. The exposure time is 1ms, the acquisition frequency is 100Hz, and the acquisition time is 30s. The collected image is a gray level image, the bit depth is 8, the gray level value range is 0 to 255, and the image resolution is 1024 pixels multiplied by 1024 pixels.
Multiple sets of test images are collected. The gray scale change rule of the collected image is analyzed, and the brightness change of the collected image is shown in figure 3. The average gray curve of the image is plotted with the order of the acquired images as abscissa and the average gray of the acquired images as ordinate, as shown in fig. 4.
The gray scale change curves of the images acquired by the left camera and the right camera are smooth, which shows that the flicker frequency of the lamp light and the acquisition frequency of the cameras are kept stable in the image acquisition process. In each set of experiments, the phase difference of the gray scale change curves of the images acquired by the left camera and the right camera is stable, which indicates that the time interval of synchronous acquisition of the left camera and the right camera is stable within the experimental time. The aliasing frequencies of the various experiments are not exactly the same, and the period of the aliasing signal is around 10s, because the lamp light flicker frequency varies slightly from experiment to experiment.
In one curve, the difference between the serial numbers of two adjacent minimum value points corresponds to the length of an aliasing signal period. The difference between the sequence numbers of the minimum value points of the left camera and the right camera corresponds to the phase difference of the aliasing signals. The time intervals at which images were acquired by the two cameras in each set of experiments were calculated as shown in table 1.
TABLE 1
Claims (3)
1. A light flicker-based two-camera synchronous acquisition time interval measurement method is characterized by comprising the following steps,
step 1: connecting two cameras with a computer respectively to form a binocular vision system;
step 2: placing the binocular vision system indoors, isolating natural light and setting a flicker light source;
and step 3: respectively setting parameters of the two cameras, aligning lenses of the cameras to a static object to enable imaging contents of the two cameras to be the same, wherein the parameters are that acquisition frequency is 100Hz, exposure time is less than 3ms, and sampling frequency of the cameras is 2 times lower than flicker frequency of lamplight;
and 4, step 4: controlling two cameras to synchronously acquire images by using a computer;
and 5: making the acquired images into average gray curves of the two cameras;
step 6: and 5, analyzing whether the acquisition frequency of the two-phase machine is stable or not through the average gray curve in the step 5, and calculating the synchronous acquisition time interval of the two-phase machine.
2. The light flicker-based two-camera synchronous acquisition time interval measurement method according to claim 1, wherein the step 6 average gray scale curve analysis process specifically comprises the steps of taking the average gray scale of the acquired image as a sampling signal, and taking the light and shade change of the light as an original signal; if the frequency of the camera is stable and the frequency of the lamplight is stable, the sampling frequency of the camera is lower than 2 times of the frequency of the original signal, and the sampling aliasing occurs according to the sampling theorem; the aliasing frequency is determined by the following equation,
wherein, f a Is the aliasing frequency; f. of s Is the original frequency; SF is the sampling frequency of the camera; int denotes a rounding function, which is an integer part of a reserved number;
n a with a value of 1, the aliasing frequency f a Satisfies the formula:
f a ＝|f s -SF| (2)
and judging whether the acquisition frequency of the camera is stable or not according to whether the average gray curve is smooth or not.
3. The light flicker-based two-camera synchronous acquisition time interval measuring method as claimed in claim 2, wherein the average gray scale of the images acquired by the two cameras is at aliasing frequency f a Making periodic variation; the average gray level curves of the images obtained by the two cameras are not overlapped, and the two curves have phase difference; assuming a phase difference of
When the images are synchronously acquired, the time interval between the two cameras for acquiring the images is delta T a (ii) a The period of light flicker is T a (ii) a If the time interval of the synchronous acquisition of the camera is less than T a Then, there are:
let the camera collect the change of brightness of the image by N t The image is one period, and the phase difference N of the average gray curve of the images collected by the two cameras a One image, the time interval between the two cameras for collecting the images is delta T a Expressed as:
in one curve, the difference of the serial numbers of two adjacent minimum value points corresponds to the length of an aliasing signal period; the difference of the sequence numbers of the minimum value points of the left camera and the right camera corresponds to the phase difference of the aliasing signals; the synchronous acquisition time interval of the two cameras is calculated by equation (4).
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102082957A (en) * | 2011-01-05 | 2011-06-01 | 清华大学 | Method and device for checking synchronism of multi-visual-angle acquisition system |
| CN102780845A (en) * | 2012-06-14 | 2012-11-14 | 清华大学 | Light source alternate strobe synchronous camera shooting method and vision detection system |
| GB201913048D0 (en) * | 2019-09-10 | 2019-10-23 | Hitomi Ltd | Signal delay measurement |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9514664B2 (en) * | 2012-09-25 | 2016-12-06 | The Boeing Company | Measuring latency in a test system using captured images |
| JP5790949B2 (en) * | 2013-02-14 | 2015-10-07 | カシオ計算機株式会社 | Camera, shooting control program, shooting control method, and camera system |
| TWI502174B (en) * | 2013-05-14 | 2015-10-01 | Pixart Imaging Inc | Optical detecting devcie and related method of synchronization adjustment |
| CN104301719B (en) * | 2014-10-29 | 2016-04-20 | 北京理工大学 | Correct the system of synchronousness in multiple stage high speed camera combined measurement system |
| KR101767662B1 (en) * | 2016-10-21 | 2017-08-14 | (주)플럭스플래닛 | Method and for synchronizing multiple camera |
| CN107463789B (en) * | 2017-08-21 | 2020-11-13 | 中国计量科学研究院 | Integrated automatic calibration device and calibration method for medical display |
| CN108965734B (en) * | 2018-09-12 | 2020-07-03 | 中国空气动力研究与发展中心超高速空气动力研究所 | Ultra-high speed imaging method based on synchronous control |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102082957A (en) * | 2011-01-05 | 2011-06-01 | 清华大学 | Method and device for checking synchronism of multi-visual-angle acquisition system |
| CN102780845A (en) * | 2012-06-14 | 2012-11-14 | 清华大学 | Light source alternate strobe synchronous camera shooting method and vision detection system |
| GB201913048D0 (en) * | 2019-09-10 | 2019-10-23 | Hitomi Ltd | Signal delay measurement |
Non-Patent Citations (1)
| Title |
|---|
| 道路监控系统中非同步相机时间校正方法;梁华刚等;《交通运输工程学报》;20150815(第04期);全文 * |
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